High frequency system



NOV; 26, v A w gs s Q HIGH FREQUENCY SYSTEM Filed May 13, 1938 In vemarsJ/freoll'enner lVa/fgqrry Hagen Patented Nov. 26, 1940 HIGH FREQUENCYSYSTEl/I Alfred Wiessner and Wolfgang Hagen, Berlin,

Germany, assignors to C. Lorenz Aktiengeselischaft, Berlin-Tempelhof,Lorenzweg, Germany,

a company ApplicationMay 13, 1938, Serial No. 207,758 In Germany May 20,1937 2 Claims.

The present invention relates to high frequency systems, and moreparticularly to an arrangement for receiving messages transmitted bymeans of high frequency carrier waves over cables.

The intelligence transmission over line networks by means of highfrequency carrier currents, the so-calledwire-radio is well known. Thesecarrier frequencies are impressed upon a telephone network, in -anexchange, office, for

instance, and are again derived from the network in the receivingpositions by the aid of electric separating filter devices. Generally, aplurality of different frequencies is simultaneously impressed upon aline network so that the receiving positions must be provided withfiltering means for again separating the various carrier frequencies. Ithas been found that the circuits employed in broadcasting'receivers ofstandard type are not sufiiciently selective for effecting 20, thenecessary separation. I It has therefore been suggested to furnishreceiving devices for wire-radio systems with band filters which areadapted to selectively be rendered effective and ineffective so as-topass merely "one single of a plurality of frequency bands, but thisexpedient becomes disadvantageous in cases that the wavelengths of atransmitter are subjected to variations, since matching to a changedwavelength involves considerable difiiculties so 30 that reliablepassing ranges will be obtained in such units only by the provision ofcomplicated expenditures. Moreover, it has been proposed to provide thereceiving positions with an oscillatory circuit the inductance of whichhaving tapping points so as to obtain adjustability to dififerentfrequencies. However, this arrangement introduces the disadvantage thatfrequency adjustments cannot be made independently of one another and,moreover, that a distinctive separa- 40 tion free of cross talkscannot-be obtained between the frequencies transmitted over cables.

These disadvantages are avoided according to the present invention whichproposes the use of adjustable oscillatory circuits in the receivingranged that one thereof acts as selective circuit equipments, saidoscillatory circuits being so arexplanatory representation with respectto certain frequency conditions, Fig. 4 diagrammatically shows acoupling circuit according to the invention, while Fig. 5diagrammatically shows still a further modification.

The Fig. 1 illustrates a correspondingarrangementwhich comprises threeresonance circuits I, 2 and 3 of the parallel type'and connected inseries. The high frequency supplied over the line is conveyed to thesecircuits over the transformer 4. Each of the three resonance circuits I,2 and 3 is tuned to one of the frequencies transmitted over the line andis connected to the succeeding portion of the receiving equipment in anysuitable manner. The received wave is derived across the resonancecircuit tuned thereto. Since the other two resonance circuits are tunedto the incoming frequencies which are to be separated, these circuitswill act as rejector, circuits so that a high quality selective effectwillbe obtained.

The Fig. 2 illustrates afparticularly suitable embodiment according tothe invention. Three resonance circuits 5, 6 and 'I of the series typeare used and connected in parallel with each other. The high frequencyincoming over the line network is applied to these circuits over thetransformer 4. The high frequency, is derived from the above mentionedresonance means between the grounded point E and the notgrounded end ofthe inductance of the oscillatory circuits. A switch 9 may, forinstance, serve for connecting these circuits to the input side of thebroadcasting receiver in. Also in this case the resonance circuitconnected to the receiver acts as selective circuit while the two othercircuits in parallel thereto act as by-pass circuits. characteristicimpedance of the line is matched to the resonance circuits by means ofthe repeater 4.

The arrangement shown in the drawing may be used as an additional memberto a standard broadcasting receiver, for instance, by providing thearrangement in a suitable box. It is also possible to utilize thisarrangement as an input circuit for a specific wire-radio receiver inwhich the tuning circuits are directly connected to the first amplifyingtube.

In cases that the arrangement would not present the required selectivityit is also within the scope of the invention to arrange the filter Thethe resonance circuits may be correspondingly tuned to the new frequencyby means of an adjustment of the condenser forming part of the circuit.

The Fig. 3 illustrates the resonance curves of the filtering circuitsshown in Figs. 1 and 2. Investigations have proven that, e. g., on usingthree frequencies of 150, 180 and 220 kilocycles differences prevailwith respect to the sharpness of the resonance curves since the widthincreases at the higher frequencies. equal curves forthese threefrequencies, a requirement which is necessary for matching thelow-frequency portion, it is possible to insert additional ohmicresistances in one or more of the resonance circuits as shown byresistances 2i and 22 in Fig. 5 which is later described in detail} orto correspondingly dimension the inductance to capacity ratio.

The higher frequency range of the low-frequency band transmitted by theagency of the carrier frequencies are generally attenuated due to theshape of the resonance curve as shown in Fig. 3. In order tocompensatethe attenuation of the higher frequencies and in accordance with afurther feature of the invention a coupling device is provided in one ofthe low-frequency stages as illustrated in Fig; 4. This figure shows atypical low frequency amplifier tube I 2. By low frequency is meant afrequency which is of a different and lower order from the frequency ofthe'wave received over the line. Thus, for example, the tube I2 mayrepresent a conventional audio frequency amplifier tube which followsthe frequency.

Still another embodiment according to the invention is shown in Fig. 5according to which a selective action corresponding to that shown inFig. 2 is accomplished in the three parallel tuning circuits H in frontof the first tube I6, while a further selective action iseffected in thethree In order to obtain serially arranged resonance circuits [9 infront of the second tube I8 which may be a tube of a detector stage. Theoutput of tube I8 is coupled by means of condenser 23 and resistance 24to a low frequency portion of the type shown in Fig. 4. The inductancecoils of the resonance members of the three serially connected selectivecircuits l9 are simultaneously employed as primary windings of repeaters20 which serve as coupling to the succeeding amplifying stage. Cores ofhigh frequency iron may be used in these repeaters in case of need. Alsoin the arrangement shown in Fig. 5, the individual circuits may beconjointly adjusted, e. g., by means of a knob common thereto.

The resonance circuits of the various stages may furthermore be somewhatde-tuned relative to one another so as to obtain a band filtering effectfor each of the three frequency ranges.

What is claimed is:

1. In a high frequency system, a receiving device for messagestransmitted over cables by means of high frequency carrier waves, saidde-. vice comprising an incoming line, a number of oscillatory circuitsarranged in stages and having inductances and capacities one of saidstages including oscillatory circuits connected in series and a furtherone of said-stages including oscillatory circuits connected in parallelto one another, a low-frequency portion having coupling means and beingcoupled to said stages, means for selectively rendering oneof saidoscillatory circuits of each stage efiective as a selective circuit andsimultaneously rendering the remainder of saidseri'es oscillatorycircuits effective as rejector cir-- cuits and the remainder of saidparalleloscilla tory circuits effective as by-pa ss circuits,andresistances included in' the individual oscillatory circuits andadapted to provide equal resonance characteristics for all oscillatorycircuits. said coupling means of said low-frequency portion beingdimensioned so as to compensate distortionsset up in the rejector andby-pass circuits.

2. In a high frequency system, a receiving de-;

vice as defined in claim 1, in which the resonance circuits in thedifferent stages are somewhatde-

